In order to maximize the efficiency of silicon solar cells, detectors or photodiodes, it is important to maximize the amount of light with a wavelength less than 1100 nm absorbed in the silicon. There are two mechanisms which can reduce the amount of light absorbed. Light may be reflected off the silicon surface, or it may enter the silicon and exit the silicon again some time later without having been absorbed. Both these loss mechanisms can be reduced by roughening, or texturing, the silicon surface. This reduces reflection losses by increasing the probability that a light ray will strike the silicon surface multiple times, and it reduces absorption losses by confining the light within the silicon (called light trapping).
A texturing technique which can be used for single crystal silicon of (100) orientation is to etch the silicon in a solution of potassium hydroxide (KOH) and isopropyl alcohol (IPA). This results in a surface covered in square base pyramids. However, this approach cannot be used for the case where the silicon surface is not (100) crystallographic orientation. Several other texturing techniques are currently under development which do not rely on a particular crystallographic orientation, such as the use of reactive ion etching (RIE). However, these techniques may prove to be expensive or to lead to other disadvantages, such as increased carrier recombination at the silicon surface. Further, these techniques are only suitable for the texturing of flat wafers and cannot be applied, for example, to the texturing of unexposed surfaces of silicon strips which are held in a wafer frame, such as strips produced as disclosed in International Patent Application no. WO 02/45143, the disclosure of which is incorporated herein by reference in its entirety.
Accordingly, there is a need for an improved process for decreasing the reflectivity of a surface of a semiconductor.
It is an object of the present invention to provide such a process.